In many valves, for example poppet valves for fuel injectors, an actuator is used to pull a spool, the poppet for example, to one of at least two positions--one in which the spool engages a seat (to open or close the valve) and one in which the spool is not engaged with the seat. In this type of valve, control of the spool's movement toward and away from its seated position is desirable. For example, it is important to ensure that at the limit of movement of the armature under the action of the solenoid, an air gap remains between the armature and the pole faces of the solenoid.
Additionally, it would be advantageous to keep the spool from slamming against the seat with its entire armature driven force all at once. This can help prevent bouncing for example, and increase product lifetime. Also, it is preferred to have the spool unseat very quickly when the valve is to move to the open valve position, in order to fully open the valve so as to get the full desired fluid flow as quickly as possible.
One valve arrangement designed to control the spool's movement is taught in U.S. Pat. No. 4,869,462 to Logie et al., issued Sep. 26, 1989. In that valve arrangement, a spool slides in a bore to a closed valve position in which the spool is engaging a seat. The spool is electromagnetically driven to the closed valve position by a solenoid with an armature. The armature is attached to a hollow coupling member that is held against the spool by a spring. When the armature pulls the spool against the seat the spool stops, but the armature and coupling member continue to move until a flange of the coupling member hits against a stop surface of an annular housing attached to the solenoid housing. The coupler spring is biased to hold the coupling member against the spool and thereby applies an additional force to keep the spool in its closed valve position.
One drawback of this design, however, is that when the coupling member stops it is resting against the housing, so that any additional force caused by the attraction of the armature-coupling member to the solenoid is lost. It would be desirable to allow that additional force to be used in keeping the spool against the seat.
This invention is directed at overcoming one or more of the above problems.